This invention relates to a superconductor particularlly usable for energy machineries or systems such as high-field magnets, current limiters, or magnetic propulsion systems.
Recently, there has been developed a superconductive material comprising a three-component metallic oxide including yttrium (Y), barium (Ba), and copper (Cu) (Y-Ba-Cu three-component metallic oxide) (for example, refer to Jpn. J. Phys. No. 26(1987)L320 and others). This three-component metallic oxide is subjected to the transposition to a superconductive material at a high temperature near or more than the liquid nitrogen temperature (77K; K: absolute temperature), thus being called a high temperature superconductor. The liquid nitrogen used as a cooling medium is cheap in price in comparison with liquid helium used conventionally, so that the fact that the critical temperature Tc thereof is of a value near or more than the liquid nitrogen temperature (77K) is very advantageous for the practical use. For example, there is known a superconductive wire material which utilizes the high temperature superconductor. The superconductive wire material which is prepared by mixing, granulating, and pre-sintering an oxide of Yttrium, barium, and copper, then crushing the thus formed oxide, filling in a sheath made of silver or the like, rolling and re-heat treating the same. The thus prepared superconductive wire material utilizing the superconductor is superior in the workability and has an excellent superconductivity, thus being suitable for a superconductor for a large and high-field magnet.
The superconductor prepared by the Y-Ba-Cu three-component metallic oxide, however, provides a problem such that the density of current passing the superconductor is small. This fact is a matter of significants in the practical use in a case where the superconductor is utilized for an energy system or machinery, and accordingly, the requirememt for the realization of a superconductor having a large current density has been increased.